Sputter ion protective apparatus



Aug 20, 1963 SPUTTER ION PROTECTIVE APPARATUS Filed May 29, 1961 INVENTORS ROBERT L.JEPSEN ARTHUR B. FRANCIS ATTORNEY R- L. JEPSEN ETAL 3,101,431

States The present invention relates to cold cathode ionization devices and more particularly to electrical sputter ion pumps.

Heretofore, electrical sputter ion pumps have been built having tor their principle of operation the establishment of a glow discharge within the interior of an open ended anode electrode disposed between and spaced from two cathode plates and having a magnetic field threaded through the anode electrode. The electron paths are modified by the magnetic field in such a way that to a considerable extent the electrons must make several collisions with gas molecules befiore they can reach the anode electrode. Some of these collisions liberate positive ions which are directed against the cathode plates where they are collected. The impinging ions also produce sputtering of the reactive cathode material which is collected upon the interior surfaces of the pump where it servesto entrap molecules in the gaseous state coming in contact therewith. .The combined effect of ion collection and sputtering serves to reduce the gas pressure'within the vessel enclosing'the cathode and anode electrodes.

Certain problems in the operation of sputter ion pumps can result from a rise in system pressure caused by exterior leaks, virtual leaks,'-evolution of gases within the system, etc. At-sufiiciently high pressures (10- mm. of Hg and above with pump geometries typically employed) very localized discharges or arcs can occur within the pump envelope concentrating large amounts of power in small areas and giving rise to themnal damage. Also, the heavy current drawn can cause pump -feed through insulators to get extremely hot so as to possibly crack, ruin external connectors, char paint on the pump body, etc. In the case of AC. pump operation these arcs or discharges may become non-rectifying to thereby further increase power dissipation within the pump envelope.

Present sputter ion pumps utilize over-current protective devices which are energized by the total current drawn from the power supply to break the circuit between supply and pump. The overcurrent protective devices have certain disadvantages because of .the normal current characteristics of the sputter ion devices. They must be bypassed during the pumps starting condition or provided with time delays so as not to be actuated by the heavy starting currents drawn. Also, these over-current devices will automatically open the power supply circuit when the pressure withina normally operating pump suddenly rises forcing the pump back into starting condition (typically, .10' l mm. of Hg). This is not always desirable since in some instances the cause of the pressure rise is a transient-occurrence and the sputter ion pump would be able to again lower the pressure of the system were it not turned oif.

The present invention utilizes an auxiliary electrode and relay circuit in a sputter .i-on pumpof the type, for

example, shown and described in U.S. application No. 673,816, now US. Patent 2,993,638. The auxiliary ciratent ice cuit draws little or no current at low pressures but will draw substantially all of the power supply current at high pressure (above 10- mm. of Hg, for example) to actuate a relay which in turn will open the power supply circuit. in the pressure region of the sputter ion pumps starting condition the auxiliary circuit will draw an insufiicientproportion of the total power supply current to actuate the protective relay.

The object of the present invention is to provide protective apparatus for sputter ion devices which will automatically distinguish between the heavy currents drawn during starting of the devices and the heavy currents drawn when operating at above starting pressures.

v 7 One feature of the present invention is the provision in a sputter ion device of an auxiliary discharge path in addition to the normal discharge path and wherein said device is further provided with separate output terminals to allow separation of the currents drawn by said auxland normal discharge paths. Another feature of the present invention is the provision in apparatus or the above featured type of an auxiliary electrode which will draw almost no current in the low pressure regions of operation but draw a high percentage of the total power supply current at pressures above 10 mm. of vHg. t

Stillanother feature or the present invention is the provision of a novel rod and cylinder electrode device which is particularly suited for operation with the above featured apparatus. I

Still another feature of the present invention is the provision in a sputter ion device of a novel high vacuum feed through insulator structure wherein an auxiliary electrode is positioned within the insulator thereby allowing the establishment of separate external circuits with a single high. vacuum teed through.

These and other features and advantages of the present invention will become more apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein,

FIG. 1 is a schematic view of one embodiment ot' the present invention,

FIG. 2 is a schematic view of another embodiment of the present invention,

FIG. 3 isa front view of a particular auxiliary electrode embodiment of the present invention,

FIG. 4 is an end view of the electrode structure shown in FIG. 3 taken along the lines 44'in the direction of the arrows, and i FIG. 5 is a side view of another auxiliary electrode structure of the present invention. I

Referring nowto FIGS. 1 and 2 the anode electrode 11- and straddling cathode plate electrodes 12 form. a primary discharge path Within the conductive vacuum envelope 1 3" The anodeelectrode 11 is connected to a source of positive potential 14- by the anode lead-in conductor '15 which is insulated from thevacuum envelope 13 by an insulator16. The cathode plate electrodes 12 are directly connected to the grounded conductive vacuum envelope 13' and the magnetic pole pieces 17 provide a mag- 0 netic field within the vacuum envelope.

An auxiliary' discharge path is provided by the auxiliary electrode gap structure 18 which has one side connected to the anode lead-in conductor 15. The other side of the auxiliary electrode structure 18 is connected to the Patented Aug. 20, 1963 p grounded relay winding 19by-the auxiliary electrode leadm conductor 21 which is insulated from the vacuum envelope 13 by an insulator 22.

As is well known in the sputter ion field, a magnetically confined glow discharge can be maintained between the cathode plate electrodes 12 and anode electrode 11 to either produce gas pumping or allow gas pressure measurement when the gas pressure within the vacuum envelope 13 is low (typically, less than mm. of Hg). However, at higher pressures the glow discharge will become unconfined and very localized arcs or discharges can occur within the vacuum envelope. These arcs and the heavy currents drawn during arcing can cause extensive thermal damage to both the sputter ion device and its power supply. The auxiliary electrode '18 is designed to draw substantially none of the power supply current when the sputter ion device is operating at starting condition pressures or below. However, at high pressures (above 10- mm. of Hg, -for example) the auxiliary electrode 18 will arc across to draw a large percentage of the current supplied by the potential source 14. This current will energize the relay winding19 which can then actuate a suitable circuit breaker (not shown) to open the circuit between power supply 14 and anode lead-in conductor 15. Since the relay winding 19 is not directly in series with the power supply 14 and anode electrode 11, it will be bypassed by the currents drawn by the primary discharge path during normal operation including starting. Similarly, the relay winding 19 will not be energized to open the power supply circuit upon the occurrence of a transient pressure rise within the vacuum envelope 13 which does not exceed the break-down pressure of the auxiliary electrode 18.

An additional advantage of this system is that the current available to actuate the relay winding 19 will be proportional to the total current supplied by the power supply 14. Thus, in large high current sputter ion devices which require large circuit breakers the available breaker actuating current will also be large.

FIG. 2. shows another embodiment of the present invention which is identical to that shown in FIG. 1 except I for the auxiliary discharge path circuit. The auxiliary electrode gap structure 23 has one side connected to the grounded vacuum envelope 13 and its other side connected "to the auxiliary electrode lead-in conductor 24 which is insulated from the envelope !13 by an insulator 25. The

trode 41. The cylindrical insulators 39 are supported by the hollow cylindrical support 43 which passes through a sputter ion device wall 42. The anode lead-in conductor 44 passes axially through the insulator assembly 38 and is supported at one end thereof by the annular support 45. The entire insulator assembly 38 is vacuum sealed and forms with the sputter ion device wall 42 a vacuum envelope. The aperture 46 in the annular electrode 41 has a larger diameter than that of the lead-in rod 44 thereby establishing a circular discharge gap between these elements within the insulator assembly 38'.

In the operation of this embodiment the anode lead-in conductor 44 is connected to a source of positive potential 47 and the annular electrode 41 is connected to the grounded sputter ion device wall 42 through a relay winding 48. The relay winding 48 will then perform the same protective function as that described for relay winding 19 of FIG. 1. An advantage gained by this particular embodiment is that only one feed through insulator is required to establish a separate exterior protective relay circuit.

Since many changes could be made in the above construction and many apparently widely difierent embodiments of'this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be. interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A cold cathode vacuum discharge apparatus comprising an anode electrode, a cathode electrode electrically insulated and spaced from said anode electrode, said anode and cathode electrodes providing a primary electron discharge path, additional electrode, means for providing an auxiliary electron discharge path, said additional electrode means including a hollow cylindrical electrode, a rod electrode extending within said hollow cylindrical electrode, and said hollow cylindrical electrode and said rod electrode form said auxiliary electron discharge path, a vacuum envelope enclosing said anode, cathode, and additional electrodes, and conductor terminal means for connecting said glow discharge device to a plurality of relay winding 19 is connected between the auxiliary leadin conductor 24 and a junction between high voltage source 14 and anode electrode lead-in 15.

The operation of this embodiment is the same as that described for FIG. 1 except that the relay winding 19 will now operate at anode rather than ground potential.

FIGS. 3 and 4 show a particular auxiliary electrode design which has been used successfully in the protective systems of FIGS. 1. and 2. A hollow cylindrical electrode 28 is supported by a bracket 29 secured to one end of a cylindrical insulator block 30 by a screw 31. A

connector bar 3-2 supporting a rod electrode 34 is attache-d to the other end of insulator block 30 by a screw 33. The rod electrode 34 extends from the conduct-or bar 32 into the cylindrical electrode 28 to form a discharge gap therein. A conductor bar 35 supporting a connector 36 is attached to the cylindrical electrode 28.

Utilizing this auxiliary gap device in the protective system of FIG. 1 the connector 36 would be connected to the anode lead-in 15 to establish the cylindrical electrode :28 at anode potential and the conductor bar 32 would be connected to the auxiliary electrode lead-in 21 establishing :a circuit between the rod electrode 34 and the relay winding .19.

FIG. 5 shows another embodiment of the present protection apparatus in which the auxiliary electrode structure is built into a feed through insulator assembly 38. Two axially aligned hollow cylindrical insulators 39 are positioned end to end and are separated by an annular elecseparate circuits outside of said envelope wherein the current drawn by said primary discharge path may be isolated from the current drawn by said auxiliary discharge path.

2. The apparatus according to claim 1 wherein said vacuum envelope is a conductor, said terminal means includes an anode lea'ddn conductor and an auxiliary leadin conductor, said anode lead-in conductor connected to said anode electrode and insulated from said vacuum envelope, said auxiliary lead-in conductor connected to said additional electrode means and insulated from said vacuum envelope, and said cathode electrode connected to said vacuum envelope.

3. The apparatus according to claim 2; including a source of potential connected to said anode lead-in conductor, and a current actuated means connected to said auxiliary lead-in conductor.

4. A cold cathode vacuum discharge apparatus cornprising an anode electrode, a cathode electrode electrically insulated and spaced from said anode electrode, said anode and cathode electrodes providing a primary electron discharge path, additional electrode means for providing an auxiliary electron discharge path, a vacuum envelope enclosing said anode electrode, cathode electrode and additional electrode means, said envelope including a hollow cylindrical feed through insulator assembly, and said additional electrode means being positioned within said feed through insulator assembly, and conductor terminal means for connecting said glow discharge device to a plurality of separate circuits outside of said envelope wherein the current drawn by said primary discharge path may be isolated from the current drawn by said auxiliary discharge path.

3,101,431 5 6 5. The apparatus according to claim 4 wherein said a current actuated means connected [to said annular elecfeed through insulator assembly includes a pair of hollow trode. cylindnical insulators sepanated by an annular electrode, 7. The apparatus according to claim :1 including a means said annular electrode having conductive portions both for supplying a magnetic field within said vacuum eninside and outside of said vacuum envelope, and an anode 5 velope.

lead-in conductor which extends through said feed through 8. The apparatus according to claim 7 including means insulator assem-hly and forms with said annular electrode for supplying potential to said anode electrode. sand auxlhary discharge P References Cited in the file of this patent 6. The apparatus according to clalm 5 including a source of potential connected to said anode lead-in conductor, and 10 UNITED STATES PATENTS 2,758,232, Fox Aug. 7, I956 

1. A COLD CATHODE VACUUM DISCHARGE APPARATUS COMPRISING AN ANODE ELECTRODE, A CATHODE ELECTRODE ELECTRICALLY INSULATED AND SPACED FROM SAID ANODE ELECTRODE, SAID ANODE AND CATHODE ELECTRODES PROVIDING A PRIMARY ELECTRON DISCHARGE PATH, ADDITIONAL ELECTRODE MEANS FOR PROVIDING AN AUXILIARY ELECTRON DISCHARGE PATH, SAID ADDITIONAL ELECTRODE MEANS INCLUDING A HOLLOW CYLINDRICAL ELECTRODE, A ROD ELECTRODE EXTENDING WITHIN SAID HOLLOW CYLINDRICAL ELECTRODE, AND SAID HOLLOW CYLINDRICAL ELECTRODE AND SAID ROD ELECTRODE FROM SAID AUXILIARY ELECTRON DISCHARGE PATH, A VACUUM ENVELOPE ENCLOSING SAID ANODE, CATHODE, AND ADDITIONAL ELECTRODES, AND CONDUCTOR TERMINAL MEANS FOR CONNECTING SAID GLOW DISCHARGE DEVICE TO A PLURALITY OF SEPARATE CIRCUITS OUTSIDE OF SAID ENVELOPE WHEREIN THE CURRENT DRAWN BY SAID PRIMARY DISCHARGE PATH MAY BE ISOLATED FROM THE CURRENT DRAWN BY SAID AUXILIARY DISCHARGE PATH. 